title: The effects of 1-amino-D-proline on the production of carnitine from exogenous protein-bound trimethyllysine by the perfused rat liver.
abstract: Following receptor-mediated endocytosis of trimethyllysine-labeled asialofetuin and agalacto-orosomucoid by liver parenchymal and nonparenchymal cells, respectively, the glycoproteins are degraded and the methylated lysine residues released. The free intracellular trimethyllysine is then converted, in addition to 2-N-acetyl-6-N-trimethyllysine, to 4-N-trimethylaminobutyrate, carnitine, and acetylcarnitine. In the presence of 1-amino-D-proline, a vitamin B6 antagonist, the total production from protein-bound trimethyllysine of 4-N-trimethylaminobutyrate, the immediate precursor of carnitine, carnitine, and its acetylated derivative was depressed by as much as 60-80% in perfused rat liver. The decreased synthesis of carnitine was accompanied by an accumulation of 3-hydroxy-6-N-trimethyllysine, and intermediate in the carnitine biosynthetic pathway. The extent of 3-hydroxy-6-N-trimethyllysine accumulation, which was not evident in the absence of added 1-amino-D-proline, depended on the dose of 1-amino-D-proline perfused through the liver. In addition, those effects of 1-amino-D-proline were almost completely reversed by inclusion of pyridoxine in the perfusing medium. These results support the suggestion of a requirement for pyridoxal 5'-phosphate in the biosynthesis of carnitine by the liver.
mesh_terms: D000818:Animals; D002331:Carnitine / Q000096:biosynthesis*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008239:Lysine / Q000031:analogs & derivatives* / Q000378:metabolism; D008297:Male; D008934:Mitogens / Q000378:metabolism*; D010477:Perfusion; D011392:Proline / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D008934:Mitogens; C003712:trimethyllysine; C012179:1-aminoproline; D011392:Proline; D008239:Lysine; D002331:Carnitine